Python之路【第二十五篇】:数据库之pymysql模块

数据库进阶

一、pymysql模块

pymysql是Python中操作Mysql的模块，其使用的方法和py2的MySQLdb几乎相同。

二、pymysql模块安装

pip install pymysql

三、执行sql语句

#_*_ coding:utf-8 _*_
# Author:Simon
# Datetime:2019/9/27 8:51
# Software:PyCharm

import pymysql

conn = pymysql.connect(host='127.0.0.1',port=3306,user='root',passwd='123456',db='lesson54')

cursor=conn.cursor()

cursor=conn.cursor(cursor=pymysql.cursors.DictCursor)  //#更改获取数据结果的数据类型,默认是元组,可以改为字典等

# sql="CREATE TABLE TEST(id INT, name VARCHAR (20))"
# cursor.execute(sql)
# cursor.execute("INSERT INTO test VALUES (3,'simon1'),(4,'zhurui1')")

//查询
row_affected=cursor.execute("SELECT * FROM test")
# one=cursor.fetchone()
# all=cursor.fetchall()
# many=cursor.fetchmany(2)

print(cursor.fetchone())
print(cursor.fetchall())
print(cursor.fetchmany())

#scroll
# cursor.scroll(-1,mode="relative")  #相对当前位置移动
# cursor.scroll(1,mode="absolute")   #相对绝对位置移动

conn.commit()  //执行完sql，首先要提交
cursor.close() //关闭终端
# conn.close() //关闭连接                

四、事务

4.1 事务命令

事务只逻辑上的一组操作，组成这组操作的各个单元，要么全部成功，要么全部不成功；

数据库开启事务命令

--        start transaction 开启事务
--        Rollback 回滚事务,即撤销指定的sql语句(只能回退insert delete update语句)，回滚到上一次commit的位置
--        Commit 提交事务，提交未存储的事务
--
--        savepoint 保留点 ，事务处理中设置的临时占位符 你可以对它发布回退(与整个事务回退不同)  

转账实例：

mysql> create table account(id int,name varchar(20),balance double);
Query OK, 0 rows affected (0.03 sec)

mysql> insert into test account values(1,"朱锐",16000);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near 'accou
nt values(1,"朱锐",16000)' at line 1
mysql> insert into account values(1,"朱锐",16000);
Query OK, 1 row affected (0.01 sec)

mysql> insert into account values(2,"simon",46000);
Query OK, 1 row affected (0.01 sec)

mysql> select * from account;
+------+--------+---------+
| id   | name   | balance |
+------+--------+---------+
|    1 | 朱锐   |   16000 |
|    2 | simon  |   46000 |
+------+--------+---------+
2 rows in set (0.00 sec)

mysql> start transaction;   //开启事务
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql> update account set balance=balance-5000 where id=1;  //转账
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from account;
+------+--------+---------+
| id   | name   | balance |
+------+--------+---------+
|    1 | 朱锐   |   11000 |
|    2 | simon  |   46000 |
+------+--------+---------+
2 rows in set (0.00 sec)

mysql>

rollback回退:

mysql> rollback;
Query OK, 0 rows affected (0.01 sec)

mysql> select * from account;
+------+--------+---------+
| id   | name   | balance |
+------+--------+---------+
|    1 | 朱锐   |   16000 |
|    2 | simon  |   46000 |
+------+--------+---------+
2 rows in set (0.00 sec)

mysql>

commit提交事务：

mysql> select * from account;
+------+--------+---------+
| id   | name   | balance |
+------+--------+---------+
|    1 | 朱锐   |   11000 |
|    2 | simon  |   46000 |
+------+--------+---------+
2 rows in set (0.00 sec)

mysql> update account set balance=balance+5000 where id=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from account;
+------+--------+---------+
| id   | name   | balance |
+------+--------+---------+
|    1 | 朱锐   |   11000 |
|    2 | simon  |   51000 |
+------+--------+---------+
2 rows in set (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql>

savepoint:

create table test2(id int PRIMARY KEY auto_increment,name VARCHAR(20)) engine=innodb;
INSERT INTO test2(name) VALUE ("simon"),
                              ("zhurui"),
                              ("caiyunjie");

start transaction;
insert into test2 (name)values('zhuruirui');
select * from test2;
commit;

-- 保留点

start transaction;
insert into test2 (name)values('huozhu');
savepoint insert_wu;
select * from test2;

delete from test2 where id=4;
savepoint delete1;
select * from test2;

delete from test2 where id=1;
savepoint delete2;
select * from test2;

rollback to delete1;

select * from test2;

savepoint

4.2 python中调用数据库启动事务的方式

import pymysql

#添加数据

conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='', db='test')

cursor = conn.cursor()

try:
    insertSQL0="INSERT INTO ACCOUNT2 (name,balance) VALUES ('caiyunjie',60000)"
    insertSQL1="UPDATE account2 set balance=balance-12700 WHERE name='simon'"
    insertSQL2="UPDATE account2 set balance=balance+12700 WHERE name='zhurui'"

    cursor = conn.cursor()

    cursor.execute(insertSQL0)
    conn.commit()

    cursor.execute(insertSQL1)
    raise Exception
    cursor.execute(insertSQL2)
    cursor.close()
    conn.commit()

except Exception as e:

    conn.rollback()
    conn.commit()

cursor.close()
conn.close()